Many modern electronic devices include wireless communications circuitry. For example, an electronic device may include wireless local area network (WLAN) communications circuitry, cellular communications circuitry, or the like. While wireless communications circuitry allows electronic devices to communicate with one another, such functionality generally comes at the cost of additional energy consumption and thus reduced battery life. Often, wireless communications circuitry is the largest consumer of energy in an electronics device. As wireless communications protocols evolve to provide higher speeds, energy consumption of communications circuitry often increases to meet the higher demands of such protocols.
Consumer demand for longer battery life from electronic devices has resulted in the development of many power-saving techniques for wireless communications. One way to conserve power consumed via wireless communications is through the use of envelope tracking. Envelope tracking involves modulating a supply voltage provided to an amplifier based on the instantaneous magnitude (i.e., the envelope) of an RF input signal provided to the amplifier. FIG. 1 illustrates the basic concept of envelope tracking. Specifically, FIG. 1 shows an amplitude-modulated RF signal 10. Conventionally, a constant supply voltage at a level sufficient to ensure adequate headroom across the entire amplitude range of the RF signal 10 would be supplied to an RF amplifier, as shown by line 12. This results in a significant amount of wasted energy, and thus poor efficiency, when the amplitude of the RF carrier is below the maximum level, as illustrated by line 14. Accordingly, an envelope power supply signal tracks the amplitude of the RF signal 10, as illustrated by line 16, and therefore increases efficiency by preventing the unnecessary expenditure of power when the amplitude of the RF signal is below the maximum level.
Generally, an envelope power supply signal should track the envelope of an RF signal from the highest peak to the lowest trough. This means that the dynamic range of the envelope tracking power supply signal must be large enough to cover the entire amplitude range of the RF signal. In general, the larger the dynamic range of the envelope power supply signal, the larger the supply voltage necessary to provide power to envelope power supply circuitry providing the envelope power supply signal. In other words, a larger dynamic range of an envelope power supply signal is generally associated with higher supply voltages and therefore higher power consumption. In order to accommodate a variety of RF signals, the supply voltage to envelope power supply circuitry is generally set based on the worst-case scenario, or the largest possible amplitude range of an RF signal. This often results in unnecessarily large supply voltages provided to an envelope power supply, which degrades efficiency and battery life.
In light of the above, there is a need for wireless communications circuitry with improved efficiency.